1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de> 4 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar 5 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner 6 * 7 * No idle tick implementation for low and high resolution timers 8 * 9 * Started by: Thomas Gleixner and Ingo Molnar 10 */ 11 #include <linux/cpu.h> 12 #include <linux/err.h> 13 #include <linux/hrtimer.h> 14 #include <linux/interrupt.h> 15 #include <linux/kernel_stat.h> 16 #include <linux/percpu.h> 17 #include <linux/nmi.h> 18 #include <linux/profile.h> 19 #include <linux/sched/signal.h> 20 #include <linux/sched/clock.h> 21 #include <linux/sched/stat.h> 22 #include <linux/sched/nohz.h> 23 #include <linux/sched/loadavg.h> 24 #include <linux/module.h> 25 #include <linux/irq_work.h> 26 #include <linux/posix-timers.h> 27 #include <linux/context_tracking.h> 28 #include <linux/mm.h> 29 30 #include <asm/irq_regs.h> 31 32 #include "tick-internal.h" 33 34 #include <trace/events/timer.h> 35 36 /* 37 * Per-CPU nohz control structure 38 */ 39 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 40 41 struct tick_sched *tick_get_tick_sched(int cpu) 42 { 43 return &per_cpu(tick_cpu_sched, cpu); 44 } 45 46 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS) 47 /* 48 * The time, when the last jiffy update happened. Write access must hold 49 * jiffies_lock and jiffies_seq. tick_nohz_next_event() needs to get a 50 * consistent view of jiffies and last_jiffies_update. 51 */ 52 static ktime_t last_jiffies_update; 53 54 /* 55 * Must be called with interrupts disabled ! 56 */ 57 static void tick_do_update_jiffies64(ktime_t now) 58 { 59 unsigned long ticks = 1; 60 ktime_t delta, nextp; 61 62 /* 63 * 64bit can do a quick check without holding jiffies lock and 64 * without looking at the sequence count. The smp_load_acquire() 65 * pairs with the update done later in this function. 66 * 67 * 32bit cannot do that because the store of tick_next_period 68 * consists of two 32bit stores and the first store could move it 69 * to a random point in the future. 70 */ 71 if (IS_ENABLED(CONFIG_64BIT)) { 72 if (ktime_before(now, smp_load_acquire(&tick_next_period))) 73 return; 74 } else { 75 unsigned int seq; 76 77 /* 78 * Avoid contention on jiffies_lock and protect the quick 79 * check with the sequence count. 80 */ 81 do { 82 seq = read_seqcount_begin(&jiffies_seq); 83 nextp = tick_next_period; 84 } while (read_seqcount_retry(&jiffies_seq, seq)); 85 86 if (ktime_before(now, nextp)) 87 return; 88 } 89 90 /* Quick check failed, i.e. update is required. */ 91 raw_spin_lock(&jiffies_lock); 92 /* 93 * Reevaluate with the lock held. Another CPU might have done the 94 * update already. 95 */ 96 if (ktime_before(now, tick_next_period)) { 97 raw_spin_unlock(&jiffies_lock); 98 return; 99 } 100 101 write_seqcount_begin(&jiffies_seq); 102 103 delta = ktime_sub(now, tick_next_period); 104 if (unlikely(delta >= TICK_NSEC)) { 105 /* Slow path for long idle sleep times */ 106 s64 incr = TICK_NSEC; 107 108 ticks += ktime_divns(delta, incr); 109 110 last_jiffies_update = ktime_add_ns(last_jiffies_update, 111 incr * ticks); 112 } else { 113 last_jiffies_update = ktime_add_ns(last_jiffies_update, 114 TICK_NSEC); 115 } 116 117 /* Advance jiffies to complete the jiffies_seq protected job */ 118 jiffies_64 += ticks; 119 120 /* 121 * Keep the tick_next_period variable up to date. 122 */ 123 nextp = ktime_add_ns(last_jiffies_update, TICK_NSEC); 124 125 if (IS_ENABLED(CONFIG_64BIT)) { 126 /* 127 * Pairs with smp_load_acquire() in the lockless quick 128 * check above and ensures that the update to jiffies_64 is 129 * not reordered vs. the store to tick_next_period, neither 130 * by the compiler nor by the CPU. 131 */ 132 smp_store_release(&tick_next_period, nextp); 133 } else { 134 /* 135 * A plain store is good enough on 32bit as the quick check 136 * above is protected by the sequence count. 137 */ 138 tick_next_period = nextp; 139 } 140 141 /* 142 * Release the sequence count. calc_global_load() below is not 143 * protected by it, but jiffies_lock needs to be held to prevent 144 * concurrent invocations. 145 */ 146 write_seqcount_end(&jiffies_seq); 147 148 calc_global_load(); 149 150 raw_spin_unlock(&jiffies_lock); 151 update_wall_time(); 152 } 153 154 /* 155 * Initialize and return retrieve the jiffies update. 156 */ 157 static ktime_t tick_init_jiffy_update(void) 158 { 159 ktime_t period; 160 161 raw_spin_lock(&jiffies_lock); 162 write_seqcount_begin(&jiffies_seq); 163 /* Did we start the jiffies update yet ? */ 164 if (last_jiffies_update == 0) 165 last_jiffies_update = tick_next_period; 166 period = last_jiffies_update; 167 write_seqcount_end(&jiffies_seq); 168 raw_spin_unlock(&jiffies_lock); 169 return period; 170 } 171 172 #define MAX_STALLED_JIFFIES 5 173 174 static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now) 175 { 176 int cpu = smp_processor_id(); 177 178 #ifdef CONFIG_NO_HZ_COMMON 179 /* 180 * Check if the do_timer duty was dropped. We don't care about 181 * concurrency: This happens only when the CPU in charge went 182 * into a long sleep. If two CPUs happen to assign themselves to 183 * this duty, then the jiffies update is still serialized by 184 * jiffies_lock. 185 * 186 * If nohz_full is enabled, this should not happen because the 187 * tick_do_timer_cpu never relinquishes. 188 */ 189 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) { 190 #ifdef CONFIG_NO_HZ_FULL 191 WARN_ON(tick_nohz_full_running); 192 #endif 193 tick_do_timer_cpu = cpu; 194 } 195 #endif 196 197 /* Check, if the jiffies need an update */ 198 if (tick_do_timer_cpu == cpu) 199 tick_do_update_jiffies64(now); 200 201 /* 202 * If jiffies update stalled for too long (timekeeper in stop_machine() 203 * or VMEXIT'ed for several msecs), force an update. 204 */ 205 if (ts->last_tick_jiffies != jiffies) { 206 ts->stalled_jiffies = 0; 207 ts->last_tick_jiffies = READ_ONCE(jiffies); 208 } else { 209 if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) { 210 tick_do_update_jiffies64(now); 211 ts->stalled_jiffies = 0; 212 ts->last_tick_jiffies = READ_ONCE(jiffies); 213 } 214 } 215 216 if (ts->inidle) 217 ts->got_idle_tick = 1; 218 } 219 220 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) 221 { 222 #ifdef CONFIG_NO_HZ_COMMON 223 /* 224 * When we are idle and the tick is stopped, we have to touch 225 * the watchdog as we might not schedule for a really long 226 * time. This happens on complete idle SMP systems while 227 * waiting on the login prompt. We also increment the "start of 228 * idle" jiffy stamp so the idle accounting adjustment we do 229 * when we go busy again does not account too much ticks. 230 */ 231 if (ts->tick_stopped) { 232 touch_softlockup_watchdog_sched(); 233 if (is_idle_task(current)) 234 ts->idle_jiffies++; 235 /* 236 * In case the current tick fired too early past its expected 237 * expiration, make sure we don't bypass the next clock reprogramming 238 * to the same deadline. 239 */ 240 ts->next_tick = 0; 241 } 242 #endif 243 update_process_times(user_mode(regs)); 244 profile_tick(CPU_PROFILING); 245 } 246 #endif 247 248 #ifdef CONFIG_NO_HZ_FULL 249 cpumask_var_t tick_nohz_full_mask; 250 EXPORT_SYMBOL_GPL(tick_nohz_full_mask); 251 bool tick_nohz_full_running; 252 EXPORT_SYMBOL_GPL(tick_nohz_full_running); 253 static atomic_t tick_dep_mask; 254 255 static bool check_tick_dependency(atomic_t *dep) 256 { 257 int val = atomic_read(dep); 258 259 if (val & TICK_DEP_MASK_POSIX_TIMER) { 260 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER); 261 return true; 262 } 263 264 if (val & TICK_DEP_MASK_PERF_EVENTS) { 265 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS); 266 return true; 267 } 268 269 if (val & TICK_DEP_MASK_SCHED) { 270 trace_tick_stop(0, TICK_DEP_MASK_SCHED); 271 return true; 272 } 273 274 if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) { 275 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE); 276 return true; 277 } 278 279 if (val & TICK_DEP_MASK_RCU) { 280 trace_tick_stop(0, TICK_DEP_MASK_RCU); 281 return true; 282 } 283 284 return false; 285 } 286 287 static bool can_stop_full_tick(int cpu, struct tick_sched *ts) 288 { 289 lockdep_assert_irqs_disabled(); 290 291 if (unlikely(!cpu_online(cpu))) 292 return false; 293 294 if (check_tick_dependency(&tick_dep_mask)) 295 return false; 296 297 if (check_tick_dependency(&ts->tick_dep_mask)) 298 return false; 299 300 if (check_tick_dependency(¤t->tick_dep_mask)) 301 return false; 302 303 if (check_tick_dependency(¤t->signal->tick_dep_mask)) 304 return false; 305 306 return true; 307 } 308 309 static void nohz_full_kick_func(struct irq_work *work) 310 { 311 /* Empty, the tick restart happens on tick_nohz_irq_exit() */ 312 } 313 314 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = 315 IRQ_WORK_INIT_HARD(nohz_full_kick_func); 316 317 /* 318 * Kick this CPU if it's full dynticks in order to force it to 319 * re-evaluate its dependency on the tick and restart it if necessary. 320 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(), 321 * is NMI safe. 322 */ 323 static void tick_nohz_full_kick(void) 324 { 325 if (!tick_nohz_full_cpu(smp_processor_id())) 326 return; 327 328 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work)); 329 } 330 331 /* 332 * Kick the CPU if it's full dynticks in order to force it to 333 * re-evaluate its dependency on the tick and restart it if necessary. 334 */ 335 void tick_nohz_full_kick_cpu(int cpu) 336 { 337 if (!tick_nohz_full_cpu(cpu)) 338 return; 339 340 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); 341 } 342 343 static void tick_nohz_kick_task(struct task_struct *tsk) 344 { 345 int cpu; 346 347 /* 348 * If the task is not running, run_posix_cpu_timers() 349 * has nothing to elapse, IPI can then be spared. 350 * 351 * activate_task() STORE p->tick_dep_mask 352 * STORE p->on_rq 353 * __schedule() (switch to task 'p') smp_mb() (atomic_fetch_or()) 354 * LOCK rq->lock LOAD p->on_rq 355 * smp_mb__after_spin_lock() 356 * tick_nohz_task_switch() 357 * LOAD p->tick_dep_mask 358 */ 359 if (!sched_task_on_rq(tsk)) 360 return; 361 362 /* 363 * If the task concurrently migrates to another CPU, 364 * we guarantee it sees the new tick dependency upon 365 * schedule. 366 * 367 * set_task_cpu(p, cpu); 368 * STORE p->cpu = @cpu 369 * __schedule() (switch to task 'p') 370 * LOCK rq->lock 371 * smp_mb__after_spin_lock() STORE p->tick_dep_mask 372 * tick_nohz_task_switch() smp_mb() (atomic_fetch_or()) 373 * LOAD p->tick_dep_mask LOAD p->cpu 374 */ 375 cpu = task_cpu(tsk); 376 377 preempt_disable(); 378 if (cpu_online(cpu)) 379 tick_nohz_full_kick_cpu(cpu); 380 preempt_enable(); 381 } 382 383 /* 384 * Kick all full dynticks CPUs in order to force these to re-evaluate 385 * their dependency on the tick and restart it if necessary. 386 */ 387 static void tick_nohz_full_kick_all(void) 388 { 389 int cpu; 390 391 if (!tick_nohz_full_running) 392 return; 393 394 preempt_disable(); 395 for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask) 396 tick_nohz_full_kick_cpu(cpu); 397 preempt_enable(); 398 } 399 400 static void tick_nohz_dep_set_all(atomic_t *dep, 401 enum tick_dep_bits bit) 402 { 403 int prev; 404 405 prev = atomic_fetch_or(BIT(bit), dep); 406 if (!prev) 407 tick_nohz_full_kick_all(); 408 } 409 410 /* 411 * Set a global tick dependency. Used by perf events that rely on freq and 412 * by unstable clock. 413 */ 414 void tick_nohz_dep_set(enum tick_dep_bits bit) 415 { 416 tick_nohz_dep_set_all(&tick_dep_mask, bit); 417 } 418 419 void tick_nohz_dep_clear(enum tick_dep_bits bit) 420 { 421 atomic_andnot(BIT(bit), &tick_dep_mask); 422 } 423 424 /* 425 * Set per-CPU tick dependency. Used by scheduler and perf events in order to 426 * manage events throttling. 427 */ 428 void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) 429 { 430 int prev; 431 struct tick_sched *ts; 432 433 ts = per_cpu_ptr(&tick_cpu_sched, cpu); 434 435 prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask); 436 if (!prev) { 437 preempt_disable(); 438 /* Perf needs local kick that is NMI safe */ 439 if (cpu == smp_processor_id()) { 440 tick_nohz_full_kick(); 441 } else { 442 /* Remote irq work not NMI-safe */ 443 if (!WARN_ON_ONCE(in_nmi())) 444 tick_nohz_full_kick_cpu(cpu); 445 } 446 preempt_enable(); 447 } 448 } 449 EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu); 450 451 void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) 452 { 453 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu); 454 455 atomic_andnot(BIT(bit), &ts->tick_dep_mask); 456 } 457 EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu); 458 459 /* 460 * Set a per-task tick dependency. RCU need this. Also posix CPU timers 461 * in order to elapse per task timers. 462 */ 463 void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit) 464 { 465 if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask)) 466 tick_nohz_kick_task(tsk); 467 } 468 EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task); 469 470 void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit) 471 { 472 atomic_andnot(BIT(bit), &tsk->tick_dep_mask); 473 } 474 EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_task); 475 476 /* 477 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse 478 * per process timers. 479 */ 480 void tick_nohz_dep_set_signal(struct task_struct *tsk, 481 enum tick_dep_bits bit) 482 { 483 int prev; 484 struct signal_struct *sig = tsk->signal; 485 486 prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask); 487 if (!prev) { 488 struct task_struct *t; 489 490 lockdep_assert_held(&tsk->sighand->siglock); 491 __for_each_thread(sig, t) 492 tick_nohz_kick_task(t); 493 } 494 } 495 496 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit) 497 { 498 atomic_andnot(BIT(bit), &sig->tick_dep_mask); 499 } 500 501 /* 502 * Re-evaluate the need for the tick as we switch the current task. 503 * It might need the tick due to per task/process properties: 504 * perf events, posix CPU timers, ... 505 */ 506 void __tick_nohz_task_switch(void) 507 { 508 struct tick_sched *ts; 509 510 if (!tick_nohz_full_cpu(smp_processor_id())) 511 return; 512 513 ts = this_cpu_ptr(&tick_cpu_sched); 514 515 if (ts->tick_stopped) { 516 if (atomic_read(¤t->tick_dep_mask) || 517 atomic_read(¤t->signal->tick_dep_mask)) 518 tick_nohz_full_kick(); 519 } 520 } 521 522 /* Get the boot-time nohz CPU list from the kernel parameters. */ 523 void __init tick_nohz_full_setup(cpumask_var_t cpumask) 524 { 525 alloc_bootmem_cpumask_var(&tick_nohz_full_mask); 526 cpumask_copy(tick_nohz_full_mask, cpumask); 527 tick_nohz_full_running = true; 528 } 529 EXPORT_SYMBOL_GPL(tick_nohz_full_setup); 530 531 static int tick_nohz_cpu_down(unsigned int cpu) 532 { 533 /* 534 * The tick_do_timer_cpu CPU handles housekeeping duty (unbound 535 * timers, workqueues, timekeeping, ...) on behalf of full dynticks 536 * CPUs. It must remain online when nohz full is enabled. 537 */ 538 if (tick_nohz_full_running && tick_do_timer_cpu == cpu) 539 return -EBUSY; 540 return 0; 541 } 542 543 void __init tick_nohz_init(void) 544 { 545 int cpu, ret; 546 547 if (!tick_nohz_full_running) 548 return; 549 550 /* 551 * Full dynticks uses irq work to drive the tick rescheduling on safe 552 * locking contexts. But then we need irq work to raise its own 553 * interrupts to avoid circular dependency on the tick 554 */ 555 if (!arch_irq_work_has_interrupt()) { 556 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n"); 557 cpumask_clear(tick_nohz_full_mask); 558 tick_nohz_full_running = false; 559 return; 560 } 561 562 if (IS_ENABLED(CONFIG_PM_SLEEP_SMP) && 563 !IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU)) { 564 cpu = smp_processor_id(); 565 566 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { 567 pr_warn("NO_HZ: Clearing %d from nohz_full range " 568 "for timekeeping\n", cpu); 569 cpumask_clear_cpu(cpu, tick_nohz_full_mask); 570 } 571 } 572 573 for_each_cpu(cpu, tick_nohz_full_mask) 574 context_tracking_cpu_set(cpu); 575 576 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, 577 "kernel/nohz:predown", NULL, 578 tick_nohz_cpu_down); 579 WARN_ON(ret < 0); 580 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", 581 cpumask_pr_args(tick_nohz_full_mask)); 582 } 583 #endif 584 585 /* 586 * NOHZ - aka dynamic tick functionality 587 */ 588 #ifdef CONFIG_NO_HZ_COMMON 589 /* 590 * NO HZ enabled ? 591 */ 592 bool tick_nohz_enabled __read_mostly = true; 593 unsigned long tick_nohz_active __read_mostly; 594 /* 595 * Enable / Disable tickless mode 596 */ 597 static int __init setup_tick_nohz(char *str) 598 { 599 return (kstrtobool(str, &tick_nohz_enabled) == 0); 600 } 601 602 __setup("nohz=", setup_tick_nohz); 603 604 bool tick_nohz_tick_stopped(void) 605 { 606 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 607 608 return ts->tick_stopped; 609 } 610 611 bool tick_nohz_tick_stopped_cpu(int cpu) 612 { 613 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu); 614 615 return ts->tick_stopped; 616 } 617 618 /** 619 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 620 * 621 * Called from interrupt entry when the CPU was idle 622 * 623 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 624 * must be updated. Otherwise an interrupt handler could use a stale jiffy 625 * value. We do this unconditionally on any CPU, as we don't know whether the 626 * CPU, which has the update task assigned is in a long sleep. 627 */ 628 static void tick_nohz_update_jiffies(ktime_t now) 629 { 630 unsigned long flags; 631 632 __this_cpu_write(tick_cpu_sched.idle_waketime, now); 633 634 local_irq_save(flags); 635 tick_do_update_jiffies64(now); 636 local_irq_restore(flags); 637 638 touch_softlockup_watchdog_sched(); 639 } 640 641 /* 642 * Updates the per-CPU time idle statistics counters 643 */ 644 static void 645 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) 646 { 647 ktime_t delta; 648 649 if (ts->idle_active) { 650 delta = ktime_sub(now, ts->idle_entrytime); 651 if (nr_iowait_cpu(cpu) > 0) 652 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); 653 else 654 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 655 ts->idle_entrytime = now; 656 } 657 658 if (last_update_time) 659 *last_update_time = ktime_to_us(now); 660 661 } 662 663 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) 664 { 665 update_ts_time_stats(smp_processor_id(), ts, now, NULL); 666 ts->idle_active = 0; 667 668 sched_clock_idle_wakeup_event(); 669 } 670 671 static void tick_nohz_start_idle(struct tick_sched *ts) 672 { 673 ts->idle_entrytime = ktime_get(); 674 ts->idle_active = 1; 675 sched_clock_idle_sleep_event(); 676 } 677 678 /** 679 * get_cpu_idle_time_us - get the total idle time of a CPU 680 * @cpu: CPU number to query 681 * @last_update_time: variable to store update time in. Do not update 682 * counters if NULL. 683 * 684 * Return the cumulative idle time (since boot) for a given 685 * CPU, in microseconds. 686 * 687 * This time is measured via accounting rather than sampling, 688 * and is as accurate as ktime_get() is. 689 * 690 * This function returns -1 if NOHZ is not enabled. 691 */ 692 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 693 { 694 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 695 ktime_t now, idle; 696 697 if (!tick_nohz_active) 698 return -1; 699 700 now = ktime_get(); 701 if (last_update_time) { 702 update_ts_time_stats(cpu, ts, now, last_update_time); 703 idle = ts->idle_sleeptime; 704 } else { 705 if (ts->idle_active && !nr_iowait_cpu(cpu)) { 706 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 707 708 idle = ktime_add(ts->idle_sleeptime, delta); 709 } else { 710 idle = ts->idle_sleeptime; 711 } 712 } 713 714 return ktime_to_us(idle); 715 716 } 717 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 718 719 /** 720 * get_cpu_iowait_time_us - get the total iowait time of a CPU 721 * @cpu: CPU number to query 722 * @last_update_time: variable to store update time in. Do not update 723 * counters if NULL. 724 * 725 * Return the cumulative iowait time (since boot) for a given 726 * CPU, in microseconds. 727 * 728 * This time is measured via accounting rather than sampling, 729 * and is as accurate as ktime_get() is. 730 * 731 * This function returns -1 if NOHZ is not enabled. 732 */ 733 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) 734 { 735 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 736 ktime_t now, iowait; 737 738 if (!tick_nohz_active) 739 return -1; 740 741 now = ktime_get(); 742 if (last_update_time) { 743 update_ts_time_stats(cpu, ts, now, last_update_time); 744 iowait = ts->iowait_sleeptime; 745 } else { 746 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { 747 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 748 749 iowait = ktime_add(ts->iowait_sleeptime, delta); 750 } else { 751 iowait = ts->iowait_sleeptime; 752 } 753 } 754 755 return ktime_to_us(iowait); 756 } 757 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); 758 759 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 760 { 761 hrtimer_cancel(&ts->sched_timer); 762 hrtimer_set_expires(&ts->sched_timer, ts->last_tick); 763 764 /* Forward the time to expire in the future */ 765 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC); 766 767 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 768 hrtimer_start_expires(&ts->sched_timer, 769 HRTIMER_MODE_ABS_PINNED_HARD); 770 } else { 771 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 772 } 773 774 /* 775 * Reset to make sure next tick stop doesn't get fooled by past 776 * cached clock deadline. 777 */ 778 ts->next_tick = 0; 779 } 780 781 static inline bool local_timer_softirq_pending(void) 782 { 783 return local_softirq_pending() & BIT(TIMER_SOFTIRQ); 784 } 785 786 static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) 787 { 788 u64 basemono, next_tick, delta, expires; 789 unsigned long basejiff; 790 unsigned int seq; 791 792 /* Read jiffies and the time when jiffies were updated last */ 793 do { 794 seq = read_seqcount_begin(&jiffies_seq); 795 basemono = last_jiffies_update; 796 basejiff = jiffies; 797 } while (read_seqcount_retry(&jiffies_seq, seq)); 798 ts->last_jiffies = basejiff; 799 ts->timer_expires_base = basemono; 800 801 /* 802 * Keep the periodic tick, when RCU, architecture or irq_work 803 * requests it. 804 * Aside of that check whether the local timer softirq is 805 * pending. If so its a bad idea to call get_next_timer_interrupt() 806 * because there is an already expired timer, so it will request 807 * immediate expiry, which rearms the hardware timer with a 808 * minimal delta which brings us back to this place 809 * immediately. Lather, rinse and repeat... 810 */ 811 if (rcu_needs_cpu() || arch_needs_cpu() || 812 irq_work_needs_cpu() || local_timer_softirq_pending()) { 813 next_tick = basemono + TICK_NSEC; 814 } else { 815 /* 816 * Get the next pending timer. If high resolution 817 * timers are enabled this only takes the timer wheel 818 * timers into account. If high resolution timers are 819 * disabled this also looks at the next expiring 820 * hrtimer. 821 */ 822 next_tick = get_next_timer_interrupt(basejiff, basemono); 823 ts->next_timer = next_tick; 824 } 825 826 /* 827 * If the tick is due in the next period, keep it ticking or 828 * force prod the timer. 829 */ 830 delta = next_tick - basemono; 831 if (delta <= (u64)TICK_NSEC) { 832 /* 833 * Tell the timer code that the base is not idle, i.e. undo 834 * the effect of get_next_timer_interrupt(): 835 */ 836 timer_clear_idle(); 837 /* 838 * We've not stopped the tick yet, and there's a timer in the 839 * next period, so no point in stopping it either, bail. 840 */ 841 if (!ts->tick_stopped) { 842 ts->timer_expires = 0; 843 goto out; 844 } 845 } 846 847 /* 848 * If this CPU is the one which had the do_timer() duty last, we limit 849 * the sleep time to the timekeeping max_deferment value. 850 * Otherwise we can sleep as long as we want. 851 */ 852 delta = timekeeping_max_deferment(); 853 if (cpu != tick_do_timer_cpu && 854 (tick_do_timer_cpu != TICK_DO_TIMER_NONE || !ts->do_timer_last)) 855 delta = KTIME_MAX; 856 857 /* Calculate the next expiry time */ 858 if (delta < (KTIME_MAX - basemono)) 859 expires = basemono + delta; 860 else 861 expires = KTIME_MAX; 862 863 ts->timer_expires = min_t(u64, expires, next_tick); 864 865 out: 866 return ts->timer_expires; 867 } 868 869 static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu) 870 { 871 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 872 u64 basemono = ts->timer_expires_base; 873 u64 expires = ts->timer_expires; 874 ktime_t tick = expires; 875 876 /* Make sure we won't be trying to stop it twice in a row. */ 877 ts->timer_expires_base = 0; 878 879 /* 880 * If this CPU is the one which updates jiffies, then give up 881 * the assignment and let it be taken by the CPU which runs 882 * the tick timer next, which might be this CPU as well. If we 883 * don't drop this here the jiffies might be stale and 884 * do_timer() never invoked. Keep track of the fact that it 885 * was the one which had the do_timer() duty last. 886 */ 887 if (cpu == tick_do_timer_cpu) { 888 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 889 ts->do_timer_last = 1; 890 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { 891 ts->do_timer_last = 0; 892 } 893 894 /* Skip reprogram of event if its not changed */ 895 if (ts->tick_stopped && (expires == ts->next_tick)) { 896 /* Sanity check: make sure clockevent is actually programmed */ 897 if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer)) 898 return; 899 900 WARN_ON_ONCE(1); 901 printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n", 902 basemono, ts->next_tick, dev->next_event, 903 hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer)); 904 } 905 906 /* 907 * nohz_stop_sched_tick can be called several times before 908 * the nohz_restart_sched_tick is called. This happens when 909 * interrupts arrive which do not cause a reschedule. In the 910 * first call we save the current tick time, so we can restart 911 * the scheduler tick in nohz_restart_sched_tick. 912 */ 913 if (!ts->tick_stopped) { 914 calc_load_nohz_start(); 915 quiet_vmstat(); 916 917 ts->last_tick = hrtimer_get_expires(&ts->sched_timer); 918 ts->tick_stopped = 1; 919 trace_tick_stop(1, TICK_DEP_MASK_NONE); 920 } 921 922 ts->next_tick = tick; 923 924 /* 925 * If the expiration time == KTIME_MAX, then we simply stop 926 * the tick timer. 927 */ 928 if (unlikely(expires == KTIME_MAX)) { 929 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 930 hrtimer_cancel(&ts->sched_timer); 931 return; 932 } 933 934 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 935 hrtimer_start(&ts->sched_timer, tick, 936 HRTIMER_MODE_ABS_PINNED_HARD); 937 } else { 938 hrtimer_set_expires(&ts->sched_timer, tick); 939 tick_program_event(tick, 1); 940 } 941 } 942 943 static void tick_nohz_retain_tick(struct tick_sched *ts) 944 { 945 ts->timer_expires_base = 0; 946 } 947 948 #ifdef CONFIG_NO_HZ_FULL 949 static void tick_nohz_stop_sched_tick(struct tick_sched *ts, int cpu) 950 { 951 if (tick_nohz_next_event(ts, cpu)) 952 tick_nohz_stop_tick(ts, cpu); 953 else 954 tick_nohz_retain_tick(ts); 955 } 956 #endif /* CONFIG_NO_HZ_FULL */ 957 958 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) 959 { 960 /* Update jiffies first */ 961 tick_do_update_jiffies64(now); 962 963 /* 964 * Clear the timer idle flag, so we avoid IPIs on remote queueing and 965 * the clock forward checks in the enqueue path: 966 */ 967 timer_clear_idle(); 968 969 calc_load_nohz_stop(); 970 touch_softlockup_watchdog_sched(); 971 /* 972 * Cancel the scheduled timer and restore the tick 973 */ 974 ts->tick_stopped = 0; 975 tick_nohz_restart(ts, now); 976 } 977 978 static void __tick_nohz_full_update_tick(struct tick_sched *ts, 979 ktime_t now) 980 { 981 #ifdef CONFIG_NO_HZ_FULL 982 int cpu = smp_processor_id(); 983 984 if (can_stop_full_tick(cpu, ts)) 985 tick_nohz_stop_sched_tick(ts, cpu); 986 else if (ts->tick_stopped) 987 tick_nohz_restart_sched_tick(ts, now); 988 #endif 989 } 990 991 static void tick_nohz_full_update_tick(struct tick_sched *ts) 992 { 993 if (!tick_nohz_full_cpu(smp_processor_id())) 994 return; 995 996 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) 997 return; 998 999 __tick_nohz_full_update_tick(ts, ktime_get()); 1000 } 1001 1002 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) 1003 { 1004 /* 1005 * If this CPU is offline and it is the one which updates 1006 * jiffies, then give up the assignment and let it be taken by 1007 * the CPU which runs the tick timer next. If we don't drop 1008 * this here the jiffies might be stale and do_timer() never 1009 * invoked. 1010 */ 1011 if (unlikely(!cpu_online(cpu))) { 1012 if (cpu == tick_do_timer_cpu) 1013 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 1014 /* 1015 * Make sure the CPU doesn't get fooled by obsolete tick 1016 * deadline if it comes back online later. 1017 */ 1018 ts->next_tick = 0; 1019 return false; 1020 } 1021 1022 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) 1023 return false; 1024 1025 if (need_resched()) 1026 return false; 1027 1028 if (unlikely(local_softirq_pending())) { 1029 static int ratelimit; 1030 1031 if (ratelimit < 10 && !local_bh_blocked() && 1032 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { 1033 pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x!!!\n", 1034 (unsigned int) local_softirq_pending()); 1035 ratelimit++; 1036 } 1037 return false; 1038 } 1039 1040 if (tick_nohz_full_enabled()) { 1041 /* 1042 * Keep the tick alive to guarantee timekeeping progression 1043 * if there are full dynticks CPUs around 1044 */ 1045 if (tick_do_timer_cpu == cpu) 1046 return false; 1047 1048 /* Should not happen for nohz-full */ 1049 if (WARN_ON_ONCE(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) 1050 return false; 1051 } 1052 1053 return true; 1054 } 1055 1056 static void __tick_nohz_idle_stop_tick(struct tick_sched *ts) 1057 { 1058 ktime_t expires; 1059 int cpu = smp_processor_id(); 1060 1061 /* 1062 * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the 1063 * tick timer expiration time is known already. 1064 */ 1065 if (ts->timer_expires_base) 1066 expires = ts->timer_expires; 1067 else if (can_stop_idle_tick(cpu, ts)) 1068 expires = tick_nohz_next_event(ts, cpu); 1069 else 1070 return; 1071 1072 ts->idle_calls++; 1073 1074 if (expires > 0LL) { 1075 int was_stopped = ts->tick_stopped; 1076 1077 tick_nohz_stop_tick(ts, cpu); 1078 1079 ts->idle_sleeps++; 1080 ts->idle_expires = expires; 1081 1082 if (!was_stopped && ts->tick_stopped) { 1083 ts->idle_jiffies = ts->last_jiffies; 1084 nohz_balance_enter_idle(cpu); 1085 } 1086 } else { 1087 tick_nohz_retain_tick(ts); 1088 } 1089 } 1090 1091 /** 1092 * tick_nohz_idle_stop_tick - stop the idle tick from the idle task 1093 * 1094 * When the next event is more than a tick into the future, stop the idle tick 1095 */ 1096 void tick_nohz_idle_stop_tick(void) 1097 { 1098 __tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched)); 1099 } 1100 1101 void tick_nohz_idle_retain_tick(void) 1102 { 1103 tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched)); 1104 /* 1105 * Undo the effect of get_next_timer_interrupt() called from 1106 * tick_nohz_next_event(). 1107 */ 1108 timer_clear_idle(); 1109 } 1110 1111 /** 1112 * tick_nohz_idle_enter - prepare for entering idle on the current CPU 1113 * 1114 * Called when we start the idle loop. 1115 */ 1116 void tick_nohz_idle_enter(void) 1117 { 1118 struct tick_sched *ts; 1119 1120 lockdep_assert_irqs_enabled(); 1121 1122 local_irq_disable(); 1123 1124 ts = this_cpu_ptr(&tick_cpu_sched); 1125 1126 WARN_ON_ONCE(ts->timer_expires_base); 1127 1128 ts->inidle = 1; 1129 tick_nohz_start_idle(ts); 1130 1131 local_irq_enable(); 1132 } 1133 1134 /** 1135 * tick_nohz_irq_exit - update next tick event from interrupt exit 1136 * 1137 * When an interrupt fires while we are idle and it doesn't cause 1138 * a reschedule, it may still add, modify or delete a timer, enqueue 1139 * an RCU callback, etc... 1140 * So we need to re-calculate and reprogram the next tick event. 1141 */ 1142 void tick_nohz_irq_exit(void) 1143 { 1144 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1145 1146 if (ts->inidle) 1147 tick_nohz_start_idle(ts); 1148 else 1149 tick_nohz_full_update_tick(ts); 1150 } 1151 1152 /** 1153 * tick_nohz_idle_got_tick - Check whether or not the tick handler has run 1154 */ 1155 bool tick_nohz_idle_got_tick(void) 1156 { 1157 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1158 1159 if (ts->got_idle_tick) { 1160 ts->got_idle_tick = 0; 1161 return true; 1162 } 1163 return false; 1164 } 1165 1166 /** 1167 * tick_nohz_get_next_hrtimer - return the next expiration time for the hrtimer 1168 * or the tick, whatever that expires first. Note that, if the tick has been 1169 * stopped, it returns the next hrtimer. 1170 * 1171 * Called from power state control code with interrupts disabled 1172 */ 1173 ktime_t tick_nohz_get_next_hrtimer(void) 1174 { 1175 return __this_cpu_read(tick_cpu_device.evtdev)->next_event; 1176 } 1177 1178 /** 1179 * tick_nohz_get_sleep_length - return the expected length of the current sleep 1180 * @delta_next: duration until the next event if the tick cannot be stopped 1181 * 1182 * Called from power state control code with interrupts disabled. 1183 * 1184 * The return value of this function and/or the value returned by it through the 1185 * @delta_next pointer can be negative which must be taken into account by its 1186 * callers. 1187 */ 1188 ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next) 1189 { 1190 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 1191 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1192 int cpu = smp_processor_id(); 1193 /* 1194 * The idle entry time is expected to be a sufficient approximation of 1195 * the current time at this point. 1196 */ 1197 ktime_t now = ts->idle_entrytime; 1198 ktime_t next_event; 1199 1200 WARN_ON_ONCE(!ts->inidle); 1201 1202 *delta_next = ktime_sub(dev->next_event, now); 1203 1204 if (!can_stop_idle_tick(cpu, ts)) 1205 return *delta_next; 1206 1207 next_event = tick_nohz_next_event(ts, cpu); 1208 if (!next_event) 1209 return *delta_next; 1210 1211 /* 1212 * If the next highres timer to expire is earlier than next_event, the 1213 * idle governor needs to know that. 1214 */ 1215 next_event = min_t(u64, next_event, 1216 hrtimer_next_event_without(&ts->sched_timer)); 1217 1218 return ktime_sub(next_event, now); 1219 } 1220 1221 /** 1222 * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value 1223 * for a particular CPU. 1224 * 1225 * Called from the schedutil frequency scaling governor in scheduler context. 1226 */ 1227 unsigned long tick_nohz_get_idle_calls_cpu(int cpu) 1228 { 1229 struct tick_sched *ts = tick_get_tick_sched(cpu); 1230 1231 return ts->idle_calls; 1232 } 1233 1234 /** 1235 * tick_nohz_get_idle_calls - return the current idle calls counter value 1236 * 1237 * Called from the schedutil frequency scaling governor in scheduler context. 1238 */ 1239 unsigned long tick_nohz_get_idle_calls(void) 1240 { 1241 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1242 1243 return ts->idle_calls; 1244 } 1245 1246 static void tick_nohz_account_idle_time(struct tick_sched *ts, 1247 ktime_t now) 1248 { 1249 unsigned long ticks; 1250 1251 ts->idle_exittime = now; 1252 1253 if (vtime_accounting_enabled_this_cpu()) 1254 return; 1255 /* 1256 * We stopped the tick in idle. Update process times would miss the 1257 * time we slept as update_process_times does only a 1 tick 1258 * accounting. Enforce that this is accounted to idle ! 1259 */ 1260 ticks = jiffies - ts->idle_jiffies; 1261 /* 1262 * We might be one off. Do not randomly account a huge number of ticks! 1263 */ 1264 if (ticks && ticks < LONG_MAX) 1265 account_idle_ticks(ticks); 1266 } 1267 1268 void tick_nohz_idle_restart_tick(void) 1269 { 1270 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1271 1272 if (ts->tick_stopped) { 1273 ktime_t now = ktime_get(); 1274 tick_nohz_restart_sched_tick(ts, now); 1275 tick_nohz_account_idle_time(ts, now); 1276 } 1277 } 1278 1279 static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now) 1280 { 1281 if (tick_nohz_full_cpu(smp_processor_id())) 1282 __tick_nohz_full_update_tick(ts, now); 1283 else 1284 tick_nohz_restart_sched_tick(ts, now); 1285 1286 tick_nohz_account_idle_time(ts, now); 1287 } 1288 1289 /** 1290 * tick_nohz_idle_exit - restart the idle tick from the idle task 1291 * 1292 * Restart the idle tick when the CPU is woken up from idle 1293 * This also exit the RCU extended quiescent state. The CPU 1294 * can use RCU again after this function is called. 1295 */ 1296 void tick_nohz_idle_exit(void) 1297 { 1298 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1299 bool idle_active, tick_stopped; 1300 ktime_t now; 1301 1302 local_irq_disable(); 1303 1304 WARN_ON_ONCE(!ts->inidle); 1305 WARN_ON_ONCE(ts->timer_expires_base); 1306 1307 ts->inidle = 0; 1308 idle_active = ts->idle_active; 1309 tick_stopped = ts->tick_stopped; 1310 1311 if (idle_active || tick_stopped) 1312 now = ktime_get(); 1313 1314 if (idle_active) 1315 tick_nohz_stop_idle(ts, now); 1316 1317 if (tick_stopped) 1318 tick_nohz_idle_update_tick(ts, now); 1319 1320 local_irq_enable(); 1321 } 1322 1323 /* 1324 * The nohz low res interrupt handler 1325 */ 1326 static void tick_nohz_handler(struct clock_event_device *dev) 1327 { 1328 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1329 struct pt_regs *regs = get_irq_regs(); 1330 ktime_t now = ktime_get(); 1331 1332 dev->next_event = KTIME_MAX; 1333 1334 tick_sched_do_timer(ts, now); 1335 tick_sched_handle(ts, regs); 1336 1337 /* No need to reprogram if we are running tickless */ 1338 if (unlikely(ts->tick_stopped)) 1339 return; 1340 1341 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC); 1342 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 1343 } 1344 1345 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) 1346 { 1347 if (!tick_nohz_enabled) 1348 return; 1349 ts->nohz_mode = mode; 1350 /* One update is enough */ 1351 if (!test_and_set_bit(0, &tick_nohz_active)) 1352 timers_update_nohz(); 1353 } 1354 1355 /** 1356 * tick_nohz_switch_to_nohz - switch to nohz mode 1357 */ 1358 static void tick_nohz_switch_to_nohz(void) 1359 { 1360 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1361 ktime_t next; 1362 1363 if (!tick_nohz_enabled) 1364 return; 1365 1366 if (tick_switch_to_oneshot(tick_nohz_handler)) 1367 return; 1368 1369 /* 1370 * Recycle the hrtimer in ts, so we can share the 1371 * hrtimer_forward with the highres code. 1372 */ 1373 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD); 1374 /* Get the next period */ 1375 next = tick_init_jiffy_update(); 1376 1377 hrtimer_set_expires(&ts->sched_timer, next); 1378 hrtimer_forward_now(&ts->sched_timer, TICK_NSEC); 1379 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 1380 tick_nohz_activate(ts, NOHZ_MODE_LOWRES); 1381 } 1382 1383 static inline void tick_nohz_irq_enter(void) 1384 { 1385 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1386 ktime_t now; 1387 1388 if (!ts->idle_active && !ts->tick_stopped) 1389 return; 1390 now = ktime_get(); 1391 if (ts->idle_active) 1392 tick_nohz_stop_idle(ts, now); 1393 /* 1394 * If all CPUs are idle. We may need to update a stale jiffies value. 1395 * Note nohz_full is a special case: a timekeeper is guaranteed to stay 1396 * alive but it might be busy looping with interrupts disabled in some 1397 * rare case (typically stop machine). So we must make sure we have a 1398 * last resort. 1399 */ 1400 if (ts->tick_stopped) 1401 tick_nohz_update_jiffies(now); 1402 } 1403 1404 #else 1405 1406 static inline void tick_nohz_switch_to_nohz(void) { } 1407 static inline void tick_nohz_irq_enter(void) { } 1408 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { } 1409 1410 #endif /* CONFIG_NO_HZ_COMMON */ 1411 1412 /* 1413 * Called from irq_enter to notify about the possible interruption of idle() 1414 */ 1415 void tick_irq_enter(void) 1416 { 1417 tick_check_oneshot_broadcast_this_cpu(); 1418 tick_nohz_irq_enter(); 1419 } 1420 1421 /* 1422 * High resolution timer specific code 1423 */ 1424 #ifdef CONFIG_HIGH_RES_TIMERS 1425 /* 1426 * We rearm the timer until we get disabled by the idle code. 1427 * Called with interrupts disabled. 1428 */ 1429 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 1430 { 1431 struct tick_sched *ts = 1432 container_of(timer, struct tick_sched, sched_timer); 1433 struct pt_regs *regs = get_irq_regs(); 1434 ktime_t now = ktime_get(); 1435 1436 tick_sched_do_timer(ts, now); 1437 1438 /* 1439 * Do not call, when we are not in irq context and have 1440 * no valid regs pointer 1441 */ 1442 if (regs) 1443 tick_sched_handle(ts, regs); 1444 else 1445 ts->next_tick = 0; 1446 1447 /* No need to reprogram if we are in idle or full dynticks mode */ 1448 if (unlikely(ts->tick_stopped)) 1449 return HRTIMER_NORESTART; 1450 1451 hrtimer_forward(timer, now, TICK_NSEC); 1452 1453 return HRTIMER_RESTART; 1454 } 1455 1456 static int sched_skew_tick; 1457 1458 static int __init skew_tick(char *str) 1459 { 1460 get_option(&str, &sched_skew_tick); 1461 1462 return 0; 1463 } 1464 early_param("skew_tick", skew_tick); 1465 1466 /** 1467 * tick_setup_sched_timer - setup the tick emulation timer 1468 */ 1469 void tick_setup_sched_timer(void) 1470 { 1471 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1472 ktime_t now = ktime_get(); 1473 1474 /* 1475 * Emulate tick processing via per-CPU hrtimers: 1476 */ 1477 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD); 1478 ts->sched_timer.function = tick_sched_timer; 1479 1480 /* Get the next period (per-CPU) */ 1481 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 1482 1483 /* Offset the tick to avert jiffies_lock contention. */ 1484 if (sched_skew_tick) { 1485 u64 offset = TICK_NSEC >> 1; 1486 do_div(offset, num_possible_cpus()); 1487 offset *= smp_processor_id(); 1488 hrtimer_add_expires_ns(&ts->sched_timer, offset); 1489 } 1490 1491 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC); 1492 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD); 1493 tick_nohz_activate(ts, NOHZ_MODE_HIGHRES); 1494 } 1495 #endif /* HIGH_RES_TIMERS */ 1496 1497 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS 1498 void tick_cancel_sched_timer(int cpu) 1499 { 1500 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 1501 1502 # ifdef CONFIG_HIGH_RES_TIMERS 1503 if (ts->sched_timer.base) 1504 hrtimer_cancel(&ts->sched_timer); 1505 # endif 1506 1507 memset(ts, 0, sizeof(*ts)); 1508 } 1509 #endif 1510 1511 /** 1512 * Async notification about clocksource changes 1513 */ 1514 void tick_clock_notify(void) 1515 { 1516 int cpu; 1517 1518 for_each_possible_cpu(cpu) 1519 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 1520 } 1521 1522 /* 1523 * Async notification about clock event changes 1524 */ 1525 void tick_oneshot_notify(void) 1526 { 1527 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1528 1529 set_bit(0, &ts->check_clocks); 1530 } 1531 1532 /** 1533 * Check, if a change happened, which makes oneshot possible. 1534 * 1535 * Called cyclic from the hrtimer softirq (driven by the timer 1536 * softirq) allow_nohz signals, that we can switch into low-res nohz 1537 * mode, because high resolution timers are disabled (either compile 1538 * or runtime). Called with interrupts disabled. 1539 */ 1540 int tick_check_oneshot_change(int allow_nohz) 1541 { 1542 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1543 1544 if (!test_and_clear_bit(0, &ts->check_clocks)) 1545 return 0; 1546 1547 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 1548 return 0; 1549 1550 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 1551 return 0; 1552 1553 if (!allow_nohz) 1554 return 1; 1555 1556 tick_nohz_switch_to_nohz(); 1557 return 0; 1558 } 1559